Synnefo » snf-image-creator

#!/usr/bin/env python

# -*- coding: utf-8 -*-

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"""This module provides the code for handling GUID partition tables"""

import struct

import sys

import uuid

import binascii

BLOCKSIZE = 512

class MBR(object):

    """Represents a Master Boot Record."""

    class Partition(object):

        """Represents a partition entry in MBR"""

        format = "<B3sB3sLL"

        def __init__(self, raw_part):

            """Create a Partition instance"""

            (

                self.status,

                self.start,

                self.type,

                self.end,

                self.first_sector,

                self.sector_count

            ) = struct.unpack(self.format, raw_part)

        def pack(self):

            """Pack the partition values into a binary string"""

            return struct.pack(self.format,

                               self.status,

                               self.start,

                               self.type,

                               self.end,

                               self.first_sector,

                               self.sector_count)

        @staticmethod

        def size():

            """Returns the size of an MBR partition entry"""

            return struct.calcsize(MBR.Partition.format)

        def __str__(self):

            start = self.unpack_chs(self.start)

            end = self.unpack_chs(self.end)

            return "%d %s %d %s %d %d" % (self.status, start, self.type, end,

                                          self.first_sector, self.sector_count)

        def unpack_chs(self, chs):

            """Unpacks a CHS address string to a tuple."""

            assert len(chs) == 3

            head = struct.unpack('<B', chs[0])[0]

            sector = struct.unpack('<B', chs[1])[0] & 0x3f

            cylinder = (struct.unpack('<B', chs[1])[0] & 0xC0) << 2 | \

                struct.unpack('<B', chs[2])[0]

            return (cylinder, head, sector)

        def pack_chs(self, cylinder, head, sector):

            """Packs a CHS tuple to an address string."""

            assert 1 <= sector <= 63

            assert 0 <= cylinder <= 1023

            assert 0 <= head <= 255

            byte0 = head

            byte1 = (cylinder >> 2) & 0xC0 | sector

            byte2 = cylinder & 0xff

            return struct.pack('<BBB', byte0, byte1, byte2)

    format = "<444s2x16s16s16s16s2s"

    """

    Offset  Length          Contents

    0       440(max. 446)   code area

    440     2(optional)     disk signature

    444     2               Usually nulls

    446     16              Partition 0

    462     16              Partition 1

    478     16              Partition 2

    494     16              Partition 3

    510     2               MBR signature

    """

    def __init__(self, block):

        """Create an MBR instance"""

        raw_part = {}

        (self.code_area,

         raw_part[0],

         raw_part[1],

         raw_part[2],

         raw_part[3],

         self.signature) = struct.unpack(self.format, block)

        self.part = {}

        for i in range(4):

            self.part[i] = self.Partition(raw_part[i])

    @staticmethod

    def size():

        """Return the size of a Master Boot Record."""

        return struct.calcsize(MBR.format)

    def pack(self):

        """Pack an MBR to a binary string."""

        return struct.pack(self.format,

                           self.code_area,

                           self.part[0].pack(),

                           self.part[1].pack(),

                           self.part[2].pack(),

                           self.part[3].pack(),

                           self.signature)

    def __str__(self):

        ret = ""

        for i in range(4):

            ret += "Partition %d: %s\n" % (i, self.part[i])

        ret += "Signature: %s %s\n" % (hex(ord(self.signature[0])),

                                       hex(ord(self.signature[1])))

        return ret

class GPTPartitionTable(object):

    """Represents a GUID Partition Table."""

    class GPTHeader(object):

        """Represents a GPT Header of a GUID Partition Table."""

        format = "<8s4sII4xQQQQ16sQIII"

        """

        Offset        Length                 Contents

        0       8 bytes         Signature

        8       4 bytes         Revision

        12      4 bytes         Header size in little endian

        16         4 bytes         CRC32 of header

        20         4 bytes         Reserved; must be zero

        24         8 bytes         Current LBA

        32         8 bytes         Backup LBA

        40         8 bytes         First usable LBA for partitions

        48         8 bytes         Last usable LBA

        56         16 bytes         Disk GUID

        72         8 bytes         Partition entries starting LBA

        80         4 bytes         Number of partition entries

        84         4 bytes         Size of a partition entry

        88         4 bytes         CRC32 of partition array

        92         *                 Reserved; must be zeroes

        LBA    size            Total

        """

        def __init__(self, block):

            """Create a GPTHeader instance"""

            (self.signature,

             self.revision,

             self.hdr_size,

             self.header_crc32,

             self.current_lba,

             self.backup_lba,

             self.first_usable_lba,

             self.last_usable_lba,

             self.uuid,

             self.part_entry_start,

             self.part_count,

             self.part_entry_size,

             self.part_crc32) = struct.unpack(self.format, block)

        def pack(self):

            """Packs a GPT Header to a binary string."""

            return struct.pack(self.format,

                               self.signature,

                               self.revision,

                               self.hdr_size,

                               self.header_crc32,

                               self.current_lba,

                               self.backup_lba,

                               self.first_usable_lba,

                               self.last_usable_lba,

                               self.uuid,

                               self.part_entry_start,

                               self.part_count,

                               self.part_entry_size,

                               self.part_crc32)

        @staticmethod

        def size():

            """Return the size of a GPT Header."""

            return struct.calcsize(GPTPartitionTable.GPTHeader.format)

        def __str__(self):

            """Print a GPTHeader"""

            return "Signature: %s\n" % self.signature + \

                   "Revision: %r\n" % self.revision + \

                   "Header Size: %d\n" % self.hdr_size + \

                   "CRC32: %d\n" % self.header_crc32 + \

                   "Current LBA: %d\n" % self.current_lba + \

                   "Backup LBA: %d\n" % self.backup_lba + \

                   "First Usable LBA: %d\n" % self.first_usable_lba + \

                   "Last Usable LBA: %d\n" % self.last_usable_lba + \

                   "Disk GUID: %s\n" % uuid.UUID(bytes=self.uuid) + \

                   "Partition entries starting LBA: %d\n" % \

                   self.part_entry_start + \

                   "Number of Partition entries: %d\n" % self.part_count + \

                   "Size of a partition entry: %d\n" % self.part_entry_size + \

                   "CRC32 of partition array: %s\n" % self.part_crc32

    def __init__(self, disk):

        """Create a GPTPartitionTable instance"""

        self.disk = disk

        with open(disk, "rb") as d:

            # MBR (Logical block address 0)

            lba0 = d.read(BLOCKSIZE)

            self.mbr = MBR(lba0)

            # Primary GPT Header (LBA 1)

            raw_header = d.read(self.GPTHeader.size())

            self.primary = self.GPTHeader(raw_header)

            # Partition entries (LBA 2...34)

            d.seek(self.primary.part_entry_start * BLOCKSIZE)

            entries_size = self.primary.part_count * \

                self.primary.part_entry_size

            self.part_entries = d.read(entries_size)

            # Secondary GPT Header (LBA -1)

            d.seek(self.primary.backup_lba * BLOCKSIZE)

            raw_header = d.read(self.GPTHeader.size())

            self.secondary = self.GPTHeader(raw_header)

    def size(self):

        """Return the payload size of GPT partitioned device."""

        return (self.primary.backup_lba + 1) * BLOCKSIZE

    def shrink(self, size, old_size):

        """Move the secondary GPT Header entries to the address specified by

        size parameter.

        """

        # Most partition manipulation programs leave 2048 sector after the last

        # partition

        aligned = size + 2048 * BLOCKSIZE

        # new_size is at least: size + Partition Entries + Secondary GPT Header

        new_size = aligned if aligned <= old_size else \

            size + len(self.part_entries) + BLOCKSIZE

        assert new_size <= old_size, "The secodary GPT fits in the device"

        if new_size == self.size():

            return new_size

        lba_count = new_size // BLOCKSIZE

        # Correct MBR

        #TODO: Check if the partition tables is hybrid

        self.mbr.part[0].sector_count = (new_size // BLOCKSIZE) - 1

        # Fix Primary header

        self.primary.header_crc32 = 0

        self.primary.backup_lba = lba_count - 1  # LBA-1

        self.primary.last_usable_lba = lba_count - 34  # LBA-34

        self.primary.header_crc32 = \

            binascii.crc32(self.primary.pack()) & 0xffffffff

        # Fix Secondary header

        self.secondary.header_crc32 = 0

        self.secondary.current_lba = self.primary.backup_lba

        self.secondary.last_usable_lba = lba_count - 34  # LBA-34

        self.secondary.part_entry_start = lba_count - 33  # LBA-33

        self.secondary.header_crc32 = \

            binascii.crc32(self.secondary.pack()) & 0xffffffff

        # Copy the new partition table back to the device

        with open(self.disk, "wb") as d:

            d.write(self.mbr.pack())

            d.write(self.primary.pack())

            d.write('\x00' * (BLOCKSIZE - self.primary.size()))

            d.write(self.part_entries)

            d.seek(self.secondary.part_entry_start * BLOCKSIZE)

            d.write(self.part_entries)

            d.seek(self.primary.backup_lba * BLOCKSIZE)

            d.write(self.secondary.pack())

            d.write('\x00' * (BLOCKSIZE - self.secondary.size()))

        return new_size

if __name__ == '__main__':

    ptable = GPTPartitionTable(sys.argv[1])

    print "MBR:\n%s" % ptable.mbr

    print "Primary partition table:\n%s" % ptable.primary

    print "Secondary partition table:\n%s" % ptable.secondary

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